22 BULLETIN 739', U. S. DEPARTMENT OF AGRICULTURE. 



colon-aerogenes group, and this one contained 3,200. After the 

 milk had been held 72 hours, 83.3 per cent were still negative in 

 1/100 cubic centimeters while 16.7 per cent were positive. The 

 colon count ranged from 1,600 to 28,000, the average being 10,533 

 per cubic centimeter. After 96 hours at 50° F. (10° C.) the same 

 percentage of the samples showed growth as after 72 hours, but the 

 average colon count was higher. 



Among the 34 samples of milk produced under dirty conditions 

 and handled in sterilized utensils 5.9 per cent showed organisms 

 of the colon-aerogenes group in 1/100 of a cubic centimeter of milk. 

 The range in colon count was from 100 to 300 and the average 200 

 per cubic centimeter. After 24 hours at 50° F. (10° C.) none of 

 the samples showed the organisms in 1/100 of a cubic centimeter. 

 This is explained by the fact that the colon count in the samples 

 which showed positive results in the fresh milk ranged from 100 to 

 300. Since 1/100 of a cubic centimeter of milk was plated this 

 meant from one to three colonies per plate, and as there was prob- 

 ably no growth during the 24-hour holding period at 50° F. (10° C), 

 these organisms were missed in a hundredth dilution on the second 

 day's plating. At the end of 72 hours only 4.4 per cent of the 

 samples showed colon-aerogenes organisms, which averaged 3,200 

 per cubic centimeter. There was a slight growth among these 

 samples between 72 and 96 hours, for, as may be noted in the 

 table, 45.8 per cent showed positive results at the end of 96 hours. 

 The colon counts ranged from 2,000 to 186,000 and averaged 24,172 

 per cubic centimeter. The results obtained in the examination of 



23 samples produced under dirty conditions and handled in un- 

 sterilized utensils agreed very closely with those just discussed. 



From these results it seems evident that there is practically no 

 growth of organisms of the colon-aerogenes group in milk produced 

 under normal conditions when it is held for a period of 48 hours at 

 50° F. (10° C). After 72 hours at this temperature there was 

 evidence of multiplication, which was still further increased by 

 holding for 96 hours. 



Duplicate samples of the milk produced under the conditions pre- 

 sented in Table 11 were held at 60° F. (15.6° C.) and the summarized 

 results are given in Table 12. It will be noted that there is a marked 

 difference in the growth of the organisms of the colon-aerogenes 

 group in milk held at the higher temperature. Quite high colon 

 counts were obtained in the majority of samples held at 60° F. (15.6° 

 C.) even in 24 hours. No further discussion of the results is neces- 

 sary, as the effect of temperature on the colon count is plainly shown 

 by the results presented. 



